by Staff Writers
Davis CA (SPX) Jan 20, 2017
Why do some trees die in a drought and others don't? And how can we predict where trees are most likely to die in future droughts? Scientists from the University of California, Davis, and colleagues examined those questions in a study published in the journal Ecology Letters.
Using climate data and aerial tree mortality surveys conducted by the U.S. Forest Service during four years (2012-2015) of extreme drought in California, they found that when a drought hits the region, trees growing in areas that are already dry are most susceptible.
The research also showed that the effects of drought on forests can take years to surface, suggesting that such effects may linger even after the drought has ended.
Southern Sierra Nevada Trees Are Most Vulnerable
The concept is simple: Trees in dense forests are like multiple straws competing for the same glass of water. In wet climate conditions, that competition goes largely unnoticed. But when it's dry, few are able to quench their thirst, setting the stage for mass mortality.
'How Much Drought A Tree Can Take'
"If forest managers want to get the biggest bang for their buck in reducing forest vulnerability to drought, this study suggests they should focus on the densest stands in the driest areas. And when we reestablish forests burned by severe wildfire in these areas, we should plant at lower densities from the beginning."
Tree mortality in the Sierra Nevada in 2015 was the worst in recorded history. The U.S. Forest Service aerial tree mortality surveys in 2015 estimated 29 million trees in California had died after four years of extreme drought.
Though the drought began in 2012, major effects on trees did not appear immediately. While some trees died every year, mortality spiked only in the fourth year of extreme drought.
Tree Mortality A Delayed Reaction
Indeed, surveys conducted by the U.S. Forest Service in 2016 estimated an additional 62 million trees died that year.
University of California - Davis
Forestry News - Global and Local News, Science and Application
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